International Publication No. WO 2013/019548 describes a series of compounds that are indicated to have inhibitory activity against chromosomal region maintenance 1 (CRM1, also referred to as exportin 1 or XPO1) and to be useful in the treatment of disorders associated with CRM1 activity, such as cancer. (Z)-3-(3-(3,5-bis(trifluoromethyl)phenyl)-1H-1,2,4-triazol-1-yl)-N′-(pyrazin-2-yl)acrylohydrazide (also referred to as selinexor) is one of the compounds disclosed in International Publication No. WO 2013/019548. Selinexor has the chemical structure shown in Structural Formula I:

The solid form of a compound can be important in the formulation of pharmaceutical compositions. For example, crystalline and amorphous forms of a compound can have different physical properties (e.g., stability, dissolution rate, density, etc.) relating to their suitability for use in pharmaceutical compositions. The difference in physical properties can also affect a crystalline or amorphous form's usefulness, for example, as an intermediate in the synthesis of a form suitable for use in pharmaceutical compositions.
There is a need for crystalline forms of Selinexor that are thermodynamically stable and suitable for use in pharmaceutical compositions (e.g. are readily dissolvable, exhibit good flow properties, have desirable particle size distribution and good chemical stability). There is a further need for crystalline forms of Selinexor having physical properties that enable the manufacture of selinexor for use in pharmaceutical compositions in high yield and high purity.